The present invention relates to a process for separating higher molecular weight constituents from phenol polymers, in particular to the separation of highermolecular compounds from optionally substituted phenol/formaldehyde condensation products.
Phenol polymers are very important raw materials for the production of molded articles and molding compounds, protective lacquers for metals or insulating materials in combination with epoxy resins. In the more recent past, they have gained importance in new fields of application, for example, as fire-resistant fibers, as support materials for ion exchangers or as binders in copying materials, such as photoresists. For these new applications the polymers must, however, meet higher requirements. Commercially available phenol polymers contain varying amounts of low-molecular constituents, which for a number of uses bring about disadvantageous effects. Thus, the processing of phenol polymers at elevated temperatures causes serious environmental problems due to the high vapor pressure of the low molecular weight constituents, so that expensive exhaust appliances must be installed. Furthermore, the relatively high content of low molecular weight compounds is responsible for the low softening temperature of phenol polymers. This serious disadvantage associated with low softening temperatures in particular affects the application of phenol polymers at elevated temperatures, for example, in their use as photoresist binders. At temperatures above about 140.degree. C. the photochemically produced structures start to flow, resulting in an undesireable, insufficient, and poor resolution.
European Patent Application No. 0 144 880 discloses a method for performing a fractionated precipitation of novolaks in order to separate off undesired, low molecular weight constituents. For this purpose, the novolaks are dissolved in a suitable solvent and reprecipitated by adding a precipitant. Thie process necessitates a careful selection of the appropriate solvents or precipitants and a strict observance of the correct temperature, in order to be able to achieve reproducible results.
German Offenlegungsschrift No. 32 22 485 (equivalent to U.S. Pat. No. 4,348,471) discloses acidfree resins. Novolaks are treated with bases, for example, tertiary amines, in order to remove, by neutralization, the acid added for the preparation of the novolaks. No fractionating of the novolaks is described.